(A) INVENTION FIELD
The invention relates the the control of an AC motor via a simple means with respect to both frequency and voltage. Utilization of a microprocessor allows for optimization of the motor controller to the motor and load therby developing a simple efficient drive system.
(B) GENERAL DESCRIPTION OF PRIOR ART
AC motor speed controllers (inverters, drives) have in the past been very large, complicated, inefficient and costly limiting the wide spred use of such a product. Technological advancements in the Microprocessor industry and the Power Semiconductor industries have lead to improvements and cost reduction of serveral of the components that make up such a controller. As kowledge on the use of motors and their applications has increased, higher performance capacities and effeciencies have become available. In addition, the use of motor speed controlers in the past have been limited to simple control, that is, manual adjustment of the speed. Recent advancements in Process Control have demanded that motor controllers become smart in their ability to communicate with other types of control equipment.
(C) OBJECT OF INVENTION
It is the object of this invention to prove that the use of a central, single Microprocessor combined with power semiconductors in a unique base drive setup, can be a simple and low cost manner in which to control Speed, Torque and Horsepower of a standard AC induction Motor at, below or above its nominal rating.
(D) SUMMARY OF THE INVENTION
The invention disclosed herein is an AC Motor Speed Controller, that provides total control over the output characteristics of the AC motor by the control of frequency and voltage to the said motor at, below or above its nominal ratings.
The invention provides the ability to control Speed of said motor throught the application of frequency applied to the motor as demanded by the controlling function. At the selected operating speed (frequency), the invention allows the voltage to be controlled to the motor which develops Torque. The combination of Speed and Torque then determines Horsepower. With individual control of both frequency and voltage, which can be preprogrammed, it allows for characterization of the output Volts per Hertz curve to the motor (output of the controller) thereby providing effective control of the Speed, Torque and Horsepower developed by the motor. Such control can be predetermined and preset or controlled by changing load conditions if programmed to do such.
To achieve the above, the controller consists of two basic sections, the Power Section and the Logic Section.
The Power Sections function is to handle all of the main power utilized by the Motor (00) itself. This consists of a Power Rectifier (20), Filter Capacitor(s) (10-23) and three Phase Modules (40,50,60). This allows for the incoming single or three phase AC to be rectified to DC and filtered. If operated off of a straight DC source, such as a battery pack, direct connection to the Phase Modules would occur. The Phase Modules, at the direction and control of the Logic Section then output and concert the DC to Variable Freqeuency and Variable Voltage (through the use of a Pulse Width Modulation Technique [PWM]) which is then outputed to the Motor (00) for control. Dynamic Braking (80) is automatically introduced on a scaled level under a controlled deceleration.
The Logic Section (30) controls the Power Section based on desired operating Speed, Current Feedback and Voltage Feedback signals and predetermined preprogrammed requirements. The Logic Section consists of the following: the Microprocessor (30-7) which is preprogrammed and active throught out the controlling function, monitoring external functions such as Current, Voltage and Speed command signals to output the appropriate signals to the driver circuits which in turn drive the three Phase Modules (40,50,60); Voltage Feedback circuit (90) monitors output voltage and outputs a voltage proportional to the output voltage of the Inverter; Current Feedback circuit (80) onitor Motor (00) current an outputs a error voltage that is proportional to the output current of the Inverter to the motor. The Electronic Fault Protector circuit (70) monitors currents in and out of the DC buss, incoming line conditions and buss voltage conditions and "shuts down" the Microprocessor (30-7) and Drivers (30-13) to the Phase Modules (40,50,60) when preset trip levels are exceeded.
The overall controller proivides a very simple and controllable means for determining the Speed, Torque and Horsepower output characteristic of the controlling AC motor.